1. Field of the Invention
This invention generally relates to a cigarette filter. More particularly, the invention relates to a cigarette filter that can selectively remove a gaseous component such as aldehydes from tobacco smoke.
2. Description of the Related Art
A wide variety of materials have been suggested in the art as filters for tobacco smoke. Such filter materials include cotton, paper, cellulose, and certain synthetic fibers. These filter materials, however, only remove particulates and condensable components from tobacco smoke. They have little or no effect in removing certain gaseous components, e.g., aldehydes, from tobacco smoke.
In light of this, a number of additives have been proposed in the art to supplement the performance of the filter materials. Exemplary additives are mentioned in, for example, U.S. Pat. Nos. 2,815,761; 2,881,772; 2,968,306; 3,003,504; and 3,354,886. Some of the additives known in the art are effective in removing certain amounts of gaseous components from tobacco smoke. However, those additives also suffer from various drawbacks.
For example, U.S. Pat. No. 2,968,306 discloses the use of certain amino acids, such as glycine, for removing aldehydes in tobacco smoke. It has been discovered that while glycine can reduce the level of formaldehyde in tobacco smoke, it is not stable in the cigarette filter manufacturing process. Moreover, it releases ammonia odor during storage.
Thus, it is an object of the present invention to provide cigarette filter arrangements and, more particularly, cigarette filters that can selectively remove a gaseous component such as aldehydes from tobacco smoke without the drawbacks or disadvantages associated with previously known additives.
It has been surprisingly discovered that a reagent comprising at least one reactive functional group covalently bonded to a non-volatile inorganic substrate is selective in removing a gaseous component such as aldehydes from tobacco smoke. It has also been surprisingly found that this system does not exhibit the drawbacks associated with additives known in the art. The reagent is preferably incorporated in a cigarette filter wherein the reactive functional group chemically reacts with a gaseous component of the smokestream to remove it from the smokestream.
The preferred functional group is an aminopropylsilyl group such as a 3-aminopropylsilyl group. The preferred substrate is in particle form, and more preferably is silica gel. The most preferred functional group/substrate arrangement (reagent) contains 3-aminopropylsilyl groups bonded to silica gel (hereinafter referred to as xe2x80x9cAPS silica gelxe2x80x9d). This reagent can selectively remove gaseous components such as polar compounds (e.g., aldehydes and hydrogen cyanide) from tobacco smoke. Other preferred reagents include aminoethylaminopropylsilyl (AEAPS) silica gel and aminoethylaminoethyl aminopropylsilyl (AEAEAPS) silica gel.
A cigarette typically contains two sections, a tobacco-containing portion sometimes referred to as the tobacco or cigarette rod, and a filter portion which may be referred to as the filter tipping. The reagent can be advantageously employed along the filter portion of the cigarette. For example, the APS silica gel can be incorporated into the filter paper, i.e., paper located in the filter portion of the cigarette. The APS silica gel can also be incorporated into the fibers of the filter portion or formed into a filter plug incorporated in the filter portion and/or the tobacco rod.